The present invention relates to increasing the rate of vulcanization of a halogenated isobutylene rubber composition.
The xe2x80x9crate of curexe2x80x9d is defined as the rate at which crosslinking and the development of the stiffness (modulus) of a rubber compound occurs. As the rubber compound is heated, the properties of the rubber compound change from a soft plastic to a tough elastic material. During the curing step, crosslinks are introduced, which connect the long polymer chains of the rubber. As more crosslinks are introduced, the polymer chains become more firmly connected and the stiffness or modulus of the compound increases. The rate of cure is an important vulcanization parameter since it in part determines the time the compound must be cured, i.e., the xe2x80x9ccure timexe2x80x9d. In the manufacture of vulcanized rubber articles, significant cost savings can be realized through a reduction of cure time. Through enhanced rates of cure, the cure time required to meet minimum states of cure can be reduced. Given the above, extensive research has been conducted in order to shorten the cure times of rubbers. Therefore, there exists a need for improved methods which enhance the rate of cure in the absence of imparting undesirable properties to the vulcanizate.
The present invention relates to the use of a sodium thiosulfate pentahydrate in a halogenated isobutylene rubber composition.
There is disclosed a method for increasing the rate of vulcanization of a halogenated isobutylene rubber composition by heating said halogenated isobutylene rubber composition to a temperature ranging from 100xc2x0 C. to 200xc2x0 C. wherein said halogenated isobutylene rubber composition contains from 0.05 to 10 phr of sodium thiosulfate pentahydrate.
There is also disclosed a halogenated isobutylene rubber composition comprising
(a) a halogenated isobutylene rubber and
(b) from 0.05 to 10 phr of a sodium thiosulfate pentahydrate.
The present invention relates to halogenated isobutylene rubber. By the term xe2x80x9chalogenated isobutylene rubberxe2x80x9d is meant a halogenated polymer comprising isobutylene subunits. Halogens include chlorine and bromine, with bromine being preferred. The halogenated rubbers used in this invention include polymers bearing halogen atoms incorporated before or after polymerization.
The halogenated isobutylene rubbers used in this invention include, but are not limited to, brominated butyl rubber (commonly called bromobutyl and abbreviated BIIR where isoprene is the diene copolymerized with isobutylene; as used herein, the term xe2x80x9cbutyl rubberxe2x80x9d means a copolymer of isobutylene and a diene such as isoprene); chlorinated butyl rubber (commonly called chlorobutyl and abbreviated CIIR where isoprene is the diene copolymerized with isobutylene); so-called star-branched polyisobutylene comprising branched or star-shaped polyisobutylene subunits, such as star-branched bromobutyl and star-branched chlorobutyl; isobutylene-bromomethylstyrene copolymers such as isobutylene/meta-bromomethylstyrene and isobutylene/para-bromomethylstyrene, isobutylene/chloromethylstyrene copolymers such as isobutylene/meta-chloromethylstyrene and isobutylene/parachloromethylstyrene, and the like, including and mixtures thereof.
The halogenated isobutylene rubbers also include halogenated isobutylene containing terpolymers, such as halogenated isobutylene/styrene/dienes; eg, isobutylene/styrene/isoprene and halogenated isobutylene/methylstyrene/dienes; eg, isobutylenelmethylstyrene/isoprene; isobutylene/halomethylstyrene/diene terpolymers including isobutylene/bromomethylstyrene/isoprene; isobutylene/haloisobutylene/dienes, including isobutylene/bromobutylene/isoprene; and the like, and mixtures thereof with other halogenated isobutylene rubbers.
The halogenated isobutylene rubber compositions of the present invention contain a majority level of a halogenated isobutylene rubber. Namely, of 100 parts by weight of total rubber in the overall composition, no less than 50 parts by weight of the halogenated isobutylene rubber per 100 parts by weight of total rubber (phr) should be used. Preferably, from 75 to 100 phr of halogenated isobutylene rubber is present.
In those instances where 100 parts by weight of halogenated isobutylene rubber is not used, other rubbers or elastomers containing olefinic unsaturation may be used in minor amounts (less than 50 parts by weight). Such rubbers or elastomers include butyl rubber, natural rubber, styrene-butadiene copolymer rubber, synthetic polyisoprene and polybutadiene.
The term xe2x80x9cphrxe2x80x9d as used herein, and according to conventional practice, refers to xe2x80x9cparts by weight of a respective material per 100 parts by weight of rubber, or elastomerxe2x80x9d.
An essential component of the present invention is the sodium thiosulfate pentahydrate. The sodium thiosulfate pentahydrate used in the present invention may be added to the rubber by any conventional technique such as on a mill or in a Banbury. The amount of sodium thiosulfate pentahydrate may vary widely depending on the type of rubber and other compounds present in the vulcanizable composition. Generally, the amount of sodium thiosulfate pentahydrate is used in a range of from about 0.05 to about 10.0 phr with a range of 0.1 to about 5.0 phr being preferred.
For ease in handling, the sodium thiosulfate pentahydrate salt may be used per se or may be deposited on suitable carriers. Examples of carriers which may be used in the present invention include silica, carbon black, alumina, kieselguhr, silica gel and calcium silicate.
The vulcanization of the halogenated isobutylene rubber composition is conducted after a sulfur vulcanizing agent has been intimately dispersed in the composition. Examples of suitable sulfur vulcanizing agents include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide or sulfur olefin adducts. Preferably, the sulfur vulcanizing agent is elemental sulfur. The sulfur vulcanizing agent may be used in an amount ranging from 0.1 to 8 phr, with a range of from 0.5 to 5.0 being preferred.
It is readily understood by those having skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the rubbers with various commonly used additive materials such as, for example, curing aids, activators, retarders, processing oils, resins, tackifying resins, plasticizers, fillers, pigments, fatty acids, zinc oxide, magnesium oxide, waxes, antioxidants, antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the halogenated isobutylene rubber composition, the additives mentioned above are selected and commonly used in conventional amounts. Typical amounts of reinforcing-type carbon blacks(s), comprise about 30 to 150 phr. Representative examples of such carbon blacks include N110, N121, N220, N231, N234, N242, N293, N299, N330, N339, N343, N347, N351, N358, N375, N660, N683, N754, N762, N765, N774, N907, N908, N990 and N991. Typical amounts of resins comprise about 0.5 to about 10 phr, usually about 1 to about 5 phr. Representative examples of such resins include phenolformaldehyde resins, hydrocarbon resins and coumaroneindene resins. Typical amounts of processing oils comprise about 1 to about 50 phr. Such processing oils can include, for example, aromatic, napthenic, and/or paraffinic processing oils. Typical amounts of antioxidants comprise about 1 to about 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in the Vanderbilt Rubber Handbook (1978), pages 344-346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of fatty acids (such as stearic acid and oleic acid) are used in an amount ranging from about 0.2 to about 3 phr. Typical amounts of zinc oxide comprise about 0.5 to about 5 phr. Typical amounts of magnesium oxide ranges from 0 to 1.0 phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often microcrystalline waxes are used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.
Accelerators may be used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. In general, from 0.1 to 3 phr of total accelerator(s) is used. Preferably, from 0.2 to 2 phr is used. In one embodiment, only a primary accelerator may be used. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts (of about 0.05 to about 1.0 phr) in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are sulfenamides, amines, disulfides, guanidines, thioureas, thiazoles, thiurams, dithiocarbamates, xanthates and mixtures thereof. If a second accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound.
The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example the ingredients are typically mixed in at least two stages, namely at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur vulcanizing agents and accelerators are typically mixed in the final stage which is conventionally called the xe2x80x9cproductivexe2x80x9d mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) of the preceding non-productive mix stage(s). The rubber and carbon black, if used, may be mixed in one or more non-productive mix stages. Preferably, the sodium thiosulfate pentahydrate is added during the nonproductive stage of mixing. The terms xe2x80x9cnon-productivexe2x80x9d and xe2x80x9cproductivexe2x80x9d mix stages are well known to those having skill in the rubber mixing art.
In one aspect of the present invention, the halogenated isobutylene rubber composition is then sulfur-cured or vulcanized.
Vulcanization of the rubber composition of the present invention is generally carried out at conventional temperatures ranging from about 100xc2x0 C. to 200xc2x0 C. Preferably, the vulcanization is conducted at temperatures ranging from about 110xc2x0 C. to 180xc2x0 C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air or in a salt bath.
Upon vulcanization of the sulfur vulcanizable composition at a temperature ranging from 100xc2x0 C. to 200xc2x0 C., the halogenated isobutylene rubber composition of this invention can be used for various purposes. For example, the halogenated isobutylene rubber composition may be in the form of a tire. In the case of a tire, it can be used for various tire components and especially in sidewalls and as an innerliner. Such tires can be built, shaped, molded and cured by various methods which are known and will be readily apparent to those having skill in such art. Preferably, the rubber composition is used in the innerliner of a tire. As can be appreciated, the tire may be a passenger tire, aircraft tire, truck tire and the like. Preferably, the tire is a passenger tire. The tire may also be a radial or bias, with a radial tire being preferred.
The invention may be better understood by reference to the following examples in which the parts and percentages are by weight unless otherwise indicated.